1. Field of the Invention
This invention relates to internal bone fixation devices which are made of very high molecular weight polymers of L(-)lactide. These devices are absorbable in the human body and need not be removed after the bone has healed.
2. Prior Art
Presently available bone fixation devices are made of metals. These metal devices are employed in severe bone fractures where it is necessary to secure the ends of the fractured bones in proximity of each other so that they may properly heal. These devices are generally in the form of intramedullary rods and pins and plates and screws. The major problem with such metal bone fixation devices is the desirability, if not necessity, of removing the devices after the bone has completely healed. The surgical procedure necessary for the removal of such devices results in additional trauma to the patient as well as increased medical costs.
It has been previously suggested that internal bone fixation devices be made of a synthetic absorbable polymer which would eliminate the necessity of the second surgical procedure to remove such fixation devices. U.S. Pat. Nos. 3,463,158; 3,636,956; 3,739,773; 3,797,499 and 3,839,297 disclose or suggest bone fixation devices made from synthetic polymers which are either polylactides, polyglycolides or copolymers of lactide and glycolide. However, prostheses made according to the teachings of these patents have been found not to have adequate load-bearing strength for the length of time that is necessary to allow their utilization as internal bone fixation devices. These prior art polymers did not maintain adequate strength for a sufficient length of time to provide the necessary load-bearing strength until the fractured bones had properly healed and could assume their normal load-bearing function.
It is believed that the polymers disclosed in the prior art were not of sufficiently high molecular weight to allow them to retain strength over the required time period, and they began to degrade and to be absorbed in the body before the bone was adequately healed and capable of assuming the normal load-bearing function.